WASHINGTON -- With sombre remembrance and steely resolve, the United States mourned its dead and its shattered innocence yesterday, even as President George W. Bush girded the nation for a new assault in his self-defined war against evil.

In a nationally televised speech last night from Ellis Island, Mr. Bush finished a day of remembrance with a harsh warning that the United States was ready to step up both its fight against terror and its determination to oust Iraqi President Saddam Hussein.

"We will not allow any terrorist or tyrant to threaten civilization with weapons of mass murder," Mr. Bush vowed in an unmistakable threat to the Baghdad regime.

The President spent the day leading the nation in mourning for those killed in the terrorist attacks of Sept. 11, 2001. He moved from the mighty granite façade of a rebuilt Pentagon to the scarred, dust-blown mass tomb of the World Trade Center site and a Pennsylvania meadow where the final hijacked plane went down, thwarted by a handful of brave passengers.

But for those who had challenged the United States, he saved his strongest words for his address at Ellis Island, gateway to generations of immigrants.

"In the ruins of two towers, under a flag unfurled at the Pentagon, at the funerals of the lost, we have made a sacred promise, to ourselves and to the world: We will not relent until justice is done and our nation is secure," he said with the brilliantly lit Statue of Liberty in the background. "What our enemies have begun, we will finish."

As it was a year ago, the President's messages throughout the day were marked more by his resolve to wage war on the enemies of the United States than by his poignant words of grief and loss.

"What happened to our nation on a September day set in motion the first great struggle of a new century," Mr. Bush said at the Pentagon yesterday morning.

"We fight, as Americans have always fought, not just for ourselves, but for the security of our friends and for peace in the world. . . . We fight to protect the innocent so that the lawless and the merciless will not inherit the Earth."

Honour guards of fire, police, military and emergency-service workers lined Mr. Bush's route earlier as he walked down a ramp into a massive, 40-hectare pit that is all that remains of the World Trade Center.

The President and first lady Laura Bush laid a wreath at the "Circle of Honour," a wooden memorial covered with flowers laid by mourners and decorated with flags and pictures of some of the thousands of victims.

In Canada, services began at sunrise in Winnipeg, where friends and family gathered to remember Christine Egan, a nurse who died in the towers while visiting her brother.

At the biggest ceremony, in Gander, Nfld., 2,500 people congregated on the airport's tarmac where a year ago 69 jetliners were forced to land as North America's airspace was shut down.

But across North America, as services were held, the day was also marked by a striking degree of normalcy, despite the heightened state of alert declared in the United States a day earlier.

Few flights were cancelled. Stock markets that were devastated last year by the terrorist attacks remained steady. And tens of millions of schoolchildren went to classes.

But with the anniversary now behind him, Mr. Bush will turn his attention today to Iraq, in a speech to the United Nations.

In a briefing for reporters yesterday, a senior Bush administration offical said the speech will lay out a case for taking on Mr. Hussein. "The President is going to make clear that the current regime is an outlaw regime, and he will rally international support for taking action to deal with the threat from Iraq because the President believes very deeply that the only option we do not have is to do nothing."

In his Ellis Island address, Mr. Bush stressed the need for "liberty" in the world, and said the United States was ready to fight for it.

He began his day with a small ceremony on the White House lawn at 8:46 -- the same minute the first silvery airliner, turned into a terrorist-guided missile, was slammed into the World Trade Center.

At the Pentagon, he rededicated a reconstructed wedge that had been ripped open by another of the hijacked airliners.

But perhaps the most poignant moment of the ceremonies was near Shanksville, near Pittsburgh, where the President mingled with relatives of the 40 passengers and crew who fought a pitched battle with four al-Qaeda terrorists to regain control of the fourth of the hijacked jets. That battle ended in a fiery crash but prevented the destruction of another target, likely the White House or the gleaming white Capitol dome in Washington.